Vertical form/fill/seal (VFFS) packaging systems have proven to be very useful in packaging a wide variety of food and non-food pumpable and/or flowable products. An example of such systems is the ONPACK™ flowable food packaging system marketed by Cryovac/Sealed Air Corporation. The VFFS process is known to those of skill in the art, and described for example in U.S. Pat. No. 4,506,494 (Shimoyama et al.), U.S. Pat. No. 4,589,247 (Tsuruta et al), U.S. Pat. No. 4,656,818 (Shimoyama et al.), U.S. Pat. No. 4,768,411 (Su), U.S. Pat. No. 4,808,010 (Vogan), and U.S. Pat. No. 5,467,581 (Everette), all incorporated herein by reference in their entirety. Typically in such a process, lay-flat thermoplastic film is advanced over a forming device to form a tube, a longitudinal (vertical) fin or lap seal is made, and a bottom end seal is made by transversely sealing across the tube with heated seal bars. A liquid, flowable, and/or pumpable product, such as a liquid, semiliquid, or paste, with or without particulates therein, is introduced through a central, vertical fill tube to the formed tubular film. Squeeze rollers spaced apart and above the bottom end seal squeeze the filled tube and pinch the walls of the flattened tube together. When a length of tubing of the desired height of the bag has been fed through the squeeze rollers a heat seal is made transversely across the flattened tubing by heat seal bars which clamp and seal the film of the tube therebetween. After the seal bars have been withdrawn the film moves downwardly to be contacted by cooled clamping and severing bars which clamp the film therebetween and are provided with a cutting knife to sever the sealed film at about the midpoint of the seal so that approximately half of the seal will be on the upper part of a tube and the other half on the lower. When the sealing and severing operation is complete, the squeeze rollers are separated to allow a new charge of product to enter the flattened tube after which the aforementioned described process is repeated thus continuously producing vertical form/fill/seal pouches which have a bottom end and top end heat seal closure.
The process can be a two-stage process where the creation of a transverse heat seal occurs at one stage in the process, and then, downstream of the first stage, a separate pair of cooling/clamping means contact the just-formed transverse heat seal to cool and thus strengthen the seal. In some VFFS processes, an upper transverse seal of a first pouch, and the lower transverse seal of a following pouch, are made, and the pouches are cut and thereby separated between two portions of the transverse seals, without the need for a separate step to clamp, cool, and cut the seals. A commercial example of an apparatus embodying this more simplified process is the ONPACK™ 2002 VFFS packaging machine marketed by Cryovac/Sealed Air Corporation.
Aseptic food packaging is a well known method of packaging foods for which sterilization of the food and the packaging material containing the food is required. It is known to produce sterilized packaging in which a sterile food product is placed in a sterilized container such as a pouch. The food product is thus preserved for later storage or use. Various methods of sterilizing the container, and filling the container with a pasteurized product, are known. Hydrogen peroxide is a common medium for sterilization of the packaging material.
In aseptic packaging applications such as vertical form fill seal pouch packaging, where hydrogen peroxide sterilization treatments are used, some films can unduly stretch after being made into a pouch and filled with the sterilized food product at elevated temperatures. These films are thus less desirable or unsuitable for this end use application where dimensional stability of the packaging material is of concern.
One current commercial packaging material for aseptic applications provides such dimensional stability, but in manufacture requires that various components of the material be laminated together. This is a relatively costly means of producing packaging materials. In the commercial laminate, biaxially oriented nylon 6 film is laminated by a conventional lamination adhesive such as polyester to a discrete multilayer substrate film. One commercial film has the construction:
LDPEAdhPA6AdhHDPEPEEVOHLDPEHDPE2.20.100.700.080.200.100.150.100.20Where the values below each resin are the layer gauge in mils, and where:    LDPE=low density polyethylene    Adh=lamination adhesive    PA6=nylon 6    HDPE=high density polyethylene    PE=polyethylene    EVOH=ethylene/vinyl alcohol copolymer
An important consideration in some aseptic packaging environments is that the packaging material exhibit good dimensional stability under load (e.g. the load of the contained food product when the packaging material is made into a package), and yet remain ductile and abuse resistant under packaging, storage, and transportation conditions. It is desirable that the packaging film possess relatively high storage modulus (E′) (ASTM D5279-01). but also possess relatively high loss modulus (E″) values at temperatures of from −150° C. to 150° C.
Copending patent application U.S. Ser. No. 11/100,739, filed 7 Apr., 2005, assigned to a common assignee with the present application, and entitled “Sterilizable Co-extruded Film For Aseptic Packaging”, now published as US 2006/0228502 A1; and copending patent application U.S. Ser. No. 11/517,728, filed 8 Sep., 2006, assigned to a common assignee with the present application, and entitled “Dimensionally Stable Sterilizable Coextruded Film For Aseptic Packaging”, now published as US 2007/0110853 A1, both publications incorporated herein by reference in their entirety, disclose coextruded multilayer films suitable for packaging products in aseptic conditions.
While these materials provide good performance in aseptic packaging, it is desirable to provide a film, for aseptic packaging, with even better oxygen barrier properties.
It is also desirable to provide a coextruded film, for pouches made in a VFFS system, that exhibits extended shelf life for the contained product by providing good oxygen barrier properties to the film and pouch made from the film.